X-ray fluoroscopic apparatus

ABSTRACT

The X-ray fluoroscopic apparatus of this invention includes a slide arm for supporting an X-ray tube, a middle slider for holding the support arm to be movable in directions along an irradiation axis of the X-ray source, and a strut for holding the middle slider to be movable the directions along the irradiation axis. Thus, compared with an amount of stroke of the X-ray tube, an amount of movement of each of the middle slider and the support arm can be small, and each of the strut, middle slider and support arm can be shortened to reduce apparatus height. Therefore, the amount of stroke of the X-ray source can be secured appropriately, while inhibiting an increase in installation space.

TECHNICAL FIELD

This invention relates to an X-ray fluoroscopic apparatus forfluoroscoping a patient, and more particularly to a technique for movingan X-ray source toward and away from an imaging device.

BACKGROUND ART

There are X-ray fluoroscopic apparatus for enabling, in addition todiagnosis of the alimentary canal including the stomach, also X-rayradiography of the chest. However, it is necessary to secure a longerdistance from an X-ray source to an imaging device (hereinafter calledFFD: Focus Film Distance as appropriate) at a time of chest radiographythan at a time of alimentary canal diagnosis. For example, it is about1.8 to 2.0 m in the case of chest radiography, as opposed to 1.1 m inthe case of alimentary canal diagnosis. FIG. 10 shows a conventionalX-ray fluoroscopic apparatus constructed to be capable of suchmultipurpose fluoroscopy. FIG. 10 shows front views of the conventionalX-ray fluoroscopic apparatus, in which (a) shows a state of a top boardbeing horizontal, (b) shows a state of the top board being inclined, and(c) shows a state of the top board being vertical. As shown, theconventional apparatus includes a tiltable top board 61 for supporting apatient M, an X-ray tube 63 disposed above the top board 61, a cassette65 disposed below the top board 61 to be opposed to the X-ray tube 63and loaded with a film, a strut 67 for supporting the cassette 65, and asupport arm 69 extendible and retractable relative to the strut 67 forholding the X-ray tube 63. The top board 61 is held by a top boardsupport (main frame) 71, and the main frame 71 is supported by apedestal 77 to be rockable through a pinion 73 and sector rack 75. Thetop board 61 tilts up and down by rotating with the main frame 71. Thestrut 67 is supported through a drive mechanism, not shown, mounted inthe main frame 71, to be movable longitudinally of the top board 61 bythe drive mechanism and rotatable with the main frame 71. The X-ray tube63 has a collimator 81 attached thereto. In an alimentary canaldiagnosis using the conventional X-ray fluoroscopic apparatusconstructed in this way, fluoroscopy is carried out with the support arm69 retracted to shorten the focus film distance. At this time, as shownin FIGS. 10 (a) and (b), the top board 61 is usually tilted with apatient M placed thereon. In a chest radiography, radiograms are takenwith the support arm 69 extended to lengthen the focus film distance. Atthis time, as shown in FIG. 10 (c), the patient M usually takes astanding position (see Patent Document 1, for example).

[Patent Document 1]

Unexamined Patent Publication No. 2005-287668

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, when an amount of sliding of the support arm 69 is increased inorder to secure a sufficient amount of stroke of the X-ray tube 63,there occurs an inconvenience of enlarging installation space.Conversely, when installation space is reduced, the amount of sliding ofthe support arm 69 will become small, which brings about aninconvenience that multipurpose fluoroscopy cannot be carried outappropriately.

This will be described specifically with reference to FIG. 11. FIG. 11shows side views of the strut and support arm according to the priorart, in which (a) shows a state of the support arm being retracted, and(b) a state of the support arm being extended. As shown in FIGS. 11 (a)and (b), between the strut 67 and support arm 69, a guide mechanism isprovided which includes a guide rail 91 and a plurality of slide blocks93. Here, in order to fully secure an amount of stroke of the X-ray tube63, the top of the support arm 69 is made higher than the X-ray tube 63to increase the amount of sliding of the support arm 69 relative to thestrut 67. In this case, the height of the apparatus is increased by anamount corresponding to the amount (i.e. the distance affixed with sign“L” in the drawings) by which the support arm 69 is made higher than theX-ray tube 63, thereby enlarging installation space for permittingtilting of the top board 61.

A restraint on apparatus height will entail a reduction in the amount ofsliding of the support arm 69 relative to the strut 67, thereby failingto secure a sufficient amount of stroke of the X-ray tube 63. As aresult, for example, when the focus film distance cannot be lengthened,a blur will occur with images obtained, which will make proper chestradiography impossible. When the focus film distance cannot beshortened, alimentary canal diagnosis cannot be carried outappropriately.

This invention has been made having regard to the state of the art notedabove, and its object is to provide an X-ray fluoroscopic apparatuscapable of appropriately securing an amount of stroke of an X-ray sourcewhile inhibiting an increase in installation space.

Means for Solving the Problem

To fulfill the above object, this invention provides the followingconstruction.

An X-ray fluoroscopic apparatus of this invention is an X-rayfluoroscopic apparatus for fluoroscoping a patient, comprising an X-raysource for emitting X rays to the patient; a support arm for supportingthe X-ray source; a middle slider for holding the support arm to bemovable along an irradiation axis of the X-ray source; and a strut forholding the middle slider to be movable along the irradiation axis.

According to the X-ray fluoroscopic apparatus of this invention, each ofthe middle slider and the support arm is movable along the irradiationaxis. Thus, the amount of movement (hereinafter called the amount ofstroke as appropriate) along the irradiation axis of the X-ray sourcecorresponds to a sum total of amounts of movement of the middle sliderand the support arm. That is, compared with the amount of stroke of theX-ray source, an amount of movement of each of the middle slider and thesupport arm can be small, and each of the strut, middle slider andsupport arm can be shortened to reduce apparatus height. Therefore, theamount of stroke of the X-ray source can be secured appropriately, whileinhibiting an increase in installation space.

In the X-ray fluoroscopic apparatus of this invention, it is preferredthat the strut has two legs formed like ridges thereon to extend alongthe irradiation axis for holding the middle slider with the legs, thesupport arm being insertable into a groove formed between the legs.Without reducing rigidity, the support arm can be retracted compactly.

In the X-ray fluoroscopic apparatus of this invention, it is preferredthat the support arm has a top portion lower than a height of the X-raysource supported by the support arm. This can curb installation space.

Preferably, the X-ray fluoroscopic apparatus of this invention furthercomprises a first guide mechanism provided between the strut and themiddle slider for guiding the middle slider along the irradiation axisrelative to the strut, and a second guide mechanism provided between themiddle slider and the support arm for guiding the support arm along theirradiation axis relative to the middle slider. The middle slider andsupport arm can be slid conveniently through the first and second guidemechanisms.

Preferably, the X-ray fluoroscopic apparatus of this invention furthercomprises a first drive device for moving the middle slider along theirradiation axis relative to the strut, and a second drive device formoving the support arm along the irradiation axis relative to the middleslider. With the first and second drive devices, the middle slider andsupport arm can be moved easily.

In the X-ray fluoroscopic apparatus of this invention, it is preferredthat the middle slider has a plurality of split slide members, the splitslide members being connected to each other to be movable along theirradiation axis, such that a space between a position where the strutholds the middle slider and a position where the middle slider holds thesupport arm is extendible and contractible. With the middle slideritself constructed telescopic, the amount of stroke of the X-ray sourceis a sum total of the amount of movement of the support arm, the amountof movement of the middle slider relative to the strut, and the amountof expansion and contraction of the middle slider itself. As a result,the amount of stroke of the X-ray source can be further increased, whilecurbing installation space.

In the X-ray fluoroscopic apparatus of this invention, it is preferredthat the strut is rotatable about a horizontal axis. Then, an alimentarycanal diagnosis, chest radiography and the like can each be carried outconveniently.

This specification discloses also the invention relating to thefollowing X-ray fluoroscopic apparatus:

(1) The X-ray fluoroscopic apparatus according to claim 4, wherein thefirst guide mechanism includes first guide rails provided on one of thestrut and the middle slider, and first slide blocks provided on theother of the strut and the middle slider to be slidable along the firstguide rails, and the second guide mechanism includes second guide railsprovided on one of the middle slider and the support arm, and secondslide blocks provided on the other of the middle slider and the supportarm to be slidable along the second guide rails.

According to the invention set out in (1) above, the first and thesecond guide mechanisms are realized conveniently.

(2) The X-ray fluoroscopic apparatus according to any one of claims 1 to7, wherein the strut further supports an imaging device in a positionopposed to the X-ray source for detecting and imaging X rays transmittedthrough the patient.

According to the invention set out in (2) above, the X-ray source andimaging device can be moved together as opposed to each other.

(3) The X-ray fluoroscopic apparatus according to any one of claims 1 to7, further comprising an imaging support device for movably supportingthe imaging device, the imaging device being movable independently ofthe X-ray source.

According to the invention set out in (3) above, the position relativeto the imaging device of the irradiation axis of the X-ray source can bemoved. This allows chest radiography to be carried out conveniently.

(4) The X-ray fluoroscopic apparatus according to any one of claims 1 to7, further comprising a first projection provided on one of the strutand the middle slider, and first restrictors provided on the other ofthe strut and the middle slider to be capable of contacting the firstprojection, for limiting a moving range of the middle slider relative tothe strut, and a second projection provided on one of the middle sliderand the support arm, and second restrictors provided on the other of themiddle slider and the support arm to be capable of contacting the secondprojection, for limiting a moving range of the support arm relative tothe middle slider.

According to the invention set out in (4) above, it is possible toprevent effectively the middle slider from falling off the strut, andthe support arm from falling off the middle slider.

EFFECTS OF THE INVENTION

According to the X-ray fluoroscopic apparatus of this invention, each ofthe middle slider and the support arm is movable along the irradiationaxis. Thus, the amount of stroke of the X-ray source corresponds to asum total of amounts of movement of the middle slider and the supportarm. That is, compared with the amount of stroke of the X-ray source, anamount of movement of each of the middle slider and the support arm canbe small, and each of the strut, middle slider and support arm can beshortened to reduce apparatus height. Therefore, the amount of stroke ofthe X-ray source can be secured appropriately, while inhibiting anincrease in installation space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows front views of an X-ray fluoroscopic apparatus according toan embodiment, in which (a), (b) and (c) show horizontal, inclined andvertical states of a top board, respectively;

FIG. 2 shows front views of a strut, a middle slider and a support arm,in which (a) shows a state of the middle slider and support arm beingretracted, (b) shows a state of the middle slider being extended and thesupport arm being retracted, and (c) shows a state of the middle sliderand support arm being extended;

FIG. 3 shows side views of the strut, middle slider and support arm, inwhich (a) shows the state of the middle slider and support arm beingretracted, (b) shows the state of the middle slider being extended andthe support arm being retracted, and (c) shows the state of the middleslider and support arm being extended;

FIG. 4 is a sectional view of the strut, middle slider and support arm;

FIG. 5 is a perspective view of the strut, middle slider and supportarm;

FIG. 6 shows front views of a strut, a middle slider and a support armaccording to a modified embodiment, in which (a) shows a state of themiddle slider and support arm being retracted, (b) shows a state of themiddle slider being extended and the support arm being retracted, and(c) shows a state of the middle slider and support arm being extended;

FIG. 7 shows side views of a strut, a middle slider and a support armaccording to a modified embodiment, in which (a) shows a state of themiddle slider and support arm being retracted, and (b) shows a state ofthe middle slider and support arm being extended;

FIG. 8 shows side views of a strut, a middle slider and a support armaccording to a modified embodiment, in which (a) shows a state of themiddle slider and support arm being retracted, and (b) shows a state ofthe middle slider and support arm being extended;

FIG. 9 is a sectional view of a strut, a middle slider and a support armaccording to a modified embodiment;

FIG. 10 shows front views of an X-ray fluoroscopic apparatus accordingto the prior art, in which (a), (b) and (c) show horizontal, inclinedand vertical states of a top board, respectively; and

FIG. 11 shows side views of a strut and a support arm according to theprior art, in which (a) shows a state of the support arm beingretracted, and (b) shows a state of the support arm being extended.

DESCRIPTION OF REFERENCES

-   5 . . . top board-   7 . . . strut-   11, 12, 13, 14 . . . middle sliders-   14 a, 14 b . . . split slide members-   15 . . . support arm-   17 . . . X-ray tube-   19 . . . cassette-   31 . . . legs-   33 . . . first guide rails-   35 . . . first slide blocks-   37 . . . second guide rails-   39 . . . second slide blocks-   41 . . . first projection-   43 . . . first restrictors-   45 . . . second projection-   47 . . . second restrictors-   51 . . . first gear-   52 . . . first motor-   53 . . . first rack-   55 . . . second gear-   56 . . . second motor-   57 . . . second rack-   M . . . patient-   P . . . irradiation axis-   A . . . groove

BEST MODE FOR CARRYING OUT THE INVENTION

In an X-ray fluoroscopic apparatus for fluoroscoping a patient, whichincludes an X-ray source for emitting X rays to the patient, a supportarm for supporting the X-ray source, a middle slider for holding thesupport arm to be movable in directions along an irradiation axis of theX-ray source, and a strut for holding the middle slider to be movable inthe directions along the irradiation axis. This construction hasfulfilled the object of appropriately securing an amount of stroke ofthe X-ray source while inhibiting an increase in installation space.

Embodiment 1

Embodiment 1 of this invention will be described hereinafter withreference to the drawings. FIG. 1 shows front views of an X-rayfluoroscopic apparatus according to the embodiment. In FIG. 1, (a), (b)and (c) show horizontal, inclined and vertical states of a top board,respectively.

The X-ray fluoroscopic apparatus according to this embodiment includes apedestal 1, a top board support (hereinafter referred to simply as themain frame) 3, a top board 5, a strut 7, a middle slider 11, a supportarm 15, an X-ray tube 17 and a cassette 19. The pedestal 1 is installedon a floor, and has a pinion 21 rotatable about a horizontal axis by adrive mechanism not shown. The main frame 3 has a sector rack (gear) 23meshed with the pinion 21, is supported by the pedestal 1, and isrotatable about a horizontal axis by rotation of the pinion 21. The topboard 5 is held by the main frame 3 to be tiltable with rotation of themain frame 3. The strut 7 is supported by the main frame 3 through adrive mechanism not shown, to be movable forward and backwardlongitudinally of the top board 5 by this drive mechanism, and rotatableabout the horizontal axis with rotation of the main frame 3. The supportarm 15 is L-shaped. The support arm 15 is supported at a proximal endthereof by the middle slider 11 to be movable in directionsperpendicular to the top board 5. The X-ray tube 17 is attached to thedistal end of the support arm 15 so that the irradiation axis P which isthe central axis of an X-ray beam emitted may extend perpendicular tothe top board 5. This X-ray tube 17 has a collimator 25 attachedthereto. The cassette 19 is held by the strut 7 in a position below thetop board 5 and opposed to the X-ray tube 17. The cassette 19 is loadedwith a film (not shown). The X-ray tube 17 and cassette 19 correspond tothe X-ray source and imaging device in this invention, respectively.

Next, the strut 7, middle slider 11 and support arm 15 will be describedin detail. FIGS. 2, 3, 4 and 5 show front views, side views, a sectionalview and a perspective view of the strut, middle slider and support arm,respectively. In FIGS. 2 and 3, (a) shows a state of the middle sliderand support arm being retracted, (b) shows a state of the middle sliderbeing extended and the support arm being retracted, and (c) shows astate of the middle slider and support arm being extended. In FIGS. 2, 3and 5, the middle slider is shown in dotted lines.

As shown, the strut 7 has a groove A formed in one side thereof toextend along the irradiation axis P of X rays, and two legs 31 formed atopposite sides of this groove A to extend in the form of ridges. Thestrut 7 in this embodiment has a sectional shape resembling letter “U”.The legs 31 have first guide rails 33 opposed to each other andextending parallel to the irradiation axis P. Each of these first guiderails 33 has first slide blocks 35 slidably attached thereto. In thisembodiment, each first guide rail 33 has two first slide blocks 35. Allthe first slide blocks 35 are fixed to the middle slider 11, whereby themiddle slider 11 is slidable relative to the strut 7. The first guiderails 33 and first slide blocks 35 will hereinafter be called the firstguide mechanism as appropriate.

The support arm 15 has a proximal region thereof with a sectional shapeslightly smaller than the sectional shape of the groove A to beaccommodatable in the groove A. The support arm 15 has two second guiderails 37 attached to one side of the proximal region thereof, to beopposed to each other and extend parallel to the first guide rails 33.Each of the second guide rails 37 also has two second slide blocks 39attached thereto. The second slide blocks 39 also are fixed to themiddle slider 11, whereby the support arm 15 is slidable relative to themiddle slider 11. The second guide rails 37 and second slide blocks 39will hereinafter be called the second guide mechanism as appropriate.

Further, the middle slider 11 has a first projection 41 formed in aposition opposed to the leg 31. In a corresponding relation thereto, theleg 31 has first restrictors 43 for contacting the first projection 41in positions where the middle slider 11 is retracted and extendedrelative to the strut 7, respectively, to limit a moving range of themiddle slider 11. Similarly, the middle slider 11 has a secondprojection 45 formed in a position opposed to the support arm 15. Thesupport arm 15 has second restrictors 47 formed in the proximal regionthereof for contacting the second projection 45 in positions where thesupport arm 15 is retracted and extended relative to the middle slider11, respectively, to limit a moving range of the support arm 15. Thesefirst and second projections 41 and 45 and first and second restrictors43 and 47 are appropriately arranged to obtain desired focus filmdistances.

Next, operation of the X-ray fluoroscopic apparatus according toEmbodiment 1 will be described. When fluoroscopy is carried out with ashortened focus film distance as in alimentary canal diagnosis, theoperator moves the middle slider 11 and support arm 15 toward the strut7 (in the direction to approach the top board 5). The middle slider 11and support arm 15 slide as guided by the first and second guide rails33 and 37, respectively. When the first projection 41 contacts the firstrestrictor 43, the middle slider 11 will stop, and no further movementin this direction will be restricted. Similarly, when the secondprojection 45 contacts the second restrictor 47, the support arm 15 willstop, and no further movement in this direction will be restricted. Inthis way, the middle slider 11 moves to a position retracted relative tothe strut 7, and moves the support arm 15 to a position retractedrelative to the middle slider 11. At this time, the proximal region ofthe support arm 15 is inserted in the groove A formed between the twolegs 31. The X-ray tube 17 and cassette 19 are in a positionalrelationship to realize a desired focus film distance (see (a) and (b)of FIGS. 2 and 3).

In this state, the pedestal 1 rotates the main frame 3, whereby the topboard 5 with the patient M placed thereon and the strut 7 rock with themain frame 3 about the horizontal axis. As a result, the position of thepatient M rotates about the horizontal axis. Based on instructions ofthe operator, the strut 7 moves longitudinally of the top board 5 asappropriate, to move the irradiation field of the X-ray tube 17 to asite of interest of the patient M. Then, the X-ray tube 17 emits X rayson instructions of the operator. The film in the cassette 19 detects Xrays transmitted through the patient M. Such fluoroscopy is carried outfor the site of interest of the patient M, while changing the positionof the patient M as appropriate.

When fluoroscopy is carried out with a lengthened focus film distance asin chest radiography, the middle slider 11 and support arm 15 are movedaway from the top board 5. The middle slider 11 slides along the firstguide rails 33 relative to the strut 7, and stops in a position wherethe first projection 41 contacts the first restrictor 43. The supportarm 15 slides along the second guide rails 37 relative to the middleslider 11, and stops in a position where the second projection 45contacts the second restrictor 47. In this way, the middle slider 11moves to a position extended relative to the strut 7, and moves thesupport arm 15 to a position extended relative to the middle slider 11.At this time, the X-ray tube 17 and cassette 19 are in a positionalrelationship to realize a desired focus film distance (see (c) of FIGS.2 and 3).

Then, the strut 7 is moved longitudinally of the top board 5 asappropriate to carry out fluoroscopy. As shown in FIG. 1 (c), in chestradiography, the top board 5 usually is erected to be vertical, and Xrays are emitted horizontally to the patient M in a standing position.

Thus, according to the X-ray fluoroscopic apparatus in this embodiment,since the middle slider 11 and support arm 15 move along the irradiationaxis P, respectively, the X-ray tube 17 moves toward and away from thecassette 19 by a distance corresponding to the sum of their amounts ofmovement. Therefore, compared with the amount of stroke of the X-raytube 17 (moving distance the X-ray tube 17 moves forward and backwardalong the irradiation axis), the amount of movement of each of themiddle slider 11 and support arm 15 is small. Consequently, each of thestrut 7, middle slider 11 and support arm 15 can be reduced in length.Since the top of the support arm 15 can be made lower than the height ofthe X-ray tube 17, it is not necessary to have a member higher than theheight of the X-ray tube 17, like the support arm included in the X-rayfluoroscopic apparatus according to the prior art. Therefore, the amountof stroke of the X-ray tube 17 can be secured appropriately, whilecurbing apparatus height and inhibiting an increase in installationspace.

The strut 7 holds the middle slider 11 with the two legs 31 formed alongthe irradiation axis P, and the support arm 15 is constructed insertablein the groove A formed between the two legs 31. Thus, without reducingthe rigidity of the strut 7, the support arm 15 can be accommodatedcompactly in the groove A when the support arm 15 is retracted.

The first guide mechanism is provided between the strut 7 and middleslider 11, and the second guide mechanism between the middle slider 11and support arm 15. This allows the middle slider 11 and support arm 15to be slidable appropriately. With the first and second guide mechanismshaving the first and second guide rails 33 and 37 and first and secondslide blocks 35 and 39, the operator can easily slide the middle slider11 and support arm 15.

Since the strut 7 is constructed rotatable about the horizontal axis,the patient M can be fluoroscoped from any angles.

Since the strut 7 holds the X-ray tube 17 and cassette 19 as opposed toeach other, the opposed relationship of the X-ray tube 17 and cassette19 is invariable even when the strut 7 moves longitudinally of the topboard 5 or rotates about the horizontal axis. Thus, fluoroscopy can becarried out conveniently.

The first and second projections 41 and 45 and the first and secondrestrictors 43 and 47 provided can prevent the middle slider 11 fromfalling off the strut 7, and the support arm 15 from falling off themiddle slider 11.

This invention is not limited to the foregoing embodiment, but may bemodified as follows:

(1) In the foregoing embodiment, the strut 7 has the groove A, and isconstructed to accommodate the support arm 15 in this groove A when thesupport arm 15 is retracted. This is not limitative. As shown in FIG. 6,the positions of first and second slide blocks 35 and 39 may be changedso that the moving range of support arm 15 may deviate from the strut 7.With this construction, the strut 7 does not need to have the groove A,which improves rigidity.

The middle slider 11 has all the first and second slide blocks 35 and 39on one surface thereof, but this is not limitative. As shown in FIG. 7,for example, a middle slider 13 may be constructed to include firstslide blocks 35 and second slide blocks 39 arranged on front and backsurfaces thereof, respectively.

Further, the middle slider 11 itself is formed of a plate-like objectwhich does not expand or contract, but this is not limitative. As shownin FIG. 8, for example, a middle slider 14 itself may be constructedtelescopic with two, large and small cylindrical split slide members 14a and 14 b connected to be slidable relative to each other along theirradiation axis P. The split slide member 14 a is held by the strut 7to be slidable along the irradiation axis P, while the split slidemember 14 b holds the support arm 15 to be slidable along theirradiation axis P. FIG. 8 illustrates a nesting structure having thesplit slide members 14 a and 14 b, strut 7 and support arm 15. With themiddle slider 14 itself constructed telescopic in this way, the spacebetween the position where the strut 7 holds the middle slider 14 andthe position where the middle slider 14 holds the support arm 15 isextendible and contractible. Thus, the amount of stroke of the X-raytube 17 is a sum total of the amount of movement of the support arm 15,the amount of movement of the middle slider 14 relative to the strut,and the amount of expansion and contraction of the middle slider 14itself. Therefore, the amount of stroke of the X-ray tube 17 can befurther increased, while curbing installation space.

(2) In the foregoing embodiment, the middle slider 11 and support arm 15are constructed manually movable by the operator. This is notlimitative. As shown in FIG. 9, for example, the strut 7 may include afirst gear 51, and a first motor 52 for rotating the first gear 51 inopposite directions, while the middle slider 11 may include a first rack53 meshed with the first gear 51, whereby the middle slider 11 ismovable relative to the strut 7. The support arm 15 may include a secondgear 55, and a second motor 56 for rotating the second gear 55 inopposite directions, while the middle slider 11 may include a secondrack 57 meshed with the second gear 55, whereby the support arm 15 ismovable relative to the middle slider 11. With this construction, themiddle slider 11 and support arm 15 can be slid easily. Here, the firstgear 51, first motor 52 and first rack 53 correspond to the first drivedevice in this invention. The second gear 55, second motor 56 and secondrack 57 correspond to the second drive device in this invention.

(3) In the foregoing embodiment, the first and second guide mechanismsare formed of the first and second guide rails 33 and 37 and first andsecond slide blocks 35 and 39. Each may be selected and modified asappropriate as long as it is a mechanism that guides the middle slideror support arm 15 along one axis (irradiation axis P).

(4) In the foregoing embodiment, the first guide rails 33 are providedon the strut 7, but this may be modified to provide them on the middleslider 11. Similarly, although the second guide rails 37 are provided onthe support arm 15, this may be modified to provide them on the middleslider 11. In such cases, the arrangement of the first and second slideblocks 35 and 39 also is changed as appropriate.

(5) In the foregoing embodiment, the middle slider 11 has the first andsecond projections 41 and 45, the leg 31 of the strut 7 has the firstrestrictors 43, and the support arm 15 has the second restrictors 47.This is not limitative. For example, a modification may be made toprovide members on the first and second guide rails 33 and 37 forcontacting the first and second slide blocks 35 and 39 to restrictfurther sliding movement.

(6) In the foregoing embodiment, the imaging device is exemplified bythe cassette 19, but this is not limitative. For example, the cassette19 may be replaced with an imaging device such as a flat panel displayor an image intensifier. In this specification, the term focus filmdistance is used because the cassette 19 is given as an example ofimaging device. This is not intended to limit the imaging device to thecassette 19. Where a flat panel display or an image intensifier is usedas the imaging device, SID (Source-Image Distance), for example, may betaken into consideration as appropriate.

(7) In the foregoing embodiment, the strut 7 is constructed to hold thecassette 19, but this is not limitative. A cassette support unit may beprovided separately from the strut 7 for movably supporting the cassette19, so that the cassette 19 may move independently of the X-ray tube 17.This can carry out chest radiography conveniently.

1. An X-ray fluoroscopic apparatus for fluoroscoping a patient,comprising an X-ray source for emitting X rays to the patient; a supportarm for supporting the X-ray source; a middle slider for holding thesupport arm to be movable along an irradiation axis of the X-ray source;and a strut for holding the middle slider to be movable along theirradiation axis.
 2. The X-ray fluoroscopic apparatus according to claim1, wherein the strut has two legs formed like ridges thereon to extendalong the irradiation axis for holding the middle slider with the legs,the support arm being insertable into a groove formed between the legs.3. The X-ray fluoroscopic apparatus according to claim 1, wherein thesupport arm has a top portion lower than a height of the X-ray sourcesupported by the support arm.
 4. The X-ray fluoroscopic apparatusaccording to claim 1, further comprising a first guide mechanismprovided between the strut and the middle slider for guiding the middleslider along the irradiation axis relative to the strut, and a secondguide mechanism provided between the middle slider and the support armfor guiding the support arm along the irradiation axis relative to themiddle slider.
 5. The X-ray fluoroscopic apparatus according to claim 1,further comprising a first drive device for moving the middle slideralong the irradiation axis relative to the strut, and a second drivedevice for moving the support arm along the irradiation axis relative tothe middle slider.
 6. The X-ray fluoroscopic apparatus according toclaim 1, wherein the middle slider has a plurality of split slidemembers, the split slide members being connected to each other to bemovable along the irradiation axis, such that a space between a positionwhere the strut holds the middle slider and a position where the middleslider holds the support arm is extendible and contractible.
 7. TheX-ray fluoroscopic apparatus according to claim 1, wherein the strut isrotatable about a horizontal axis.